Microorganisms in a Macro World (part 3)

mbeall

CHIN, Gatineau, Quebec

5. High osmotic pressure

Addition of sugar

Water is removed from microbial cells when they are placed in solutions containing large quantities of sugar. This inhibits the microorganisms’ growth but does not kill them. Yeasts and fungi are more resistant than bacteria to high osmotic pressure. This is why it is more common to see jellies and jams contaminated with microscopic fungi rather than bacteria after being exposed to air. Condensed milk is also preserved due to high concentrations of lactose and sucrose, which also remove water from microbial cells.

Addition of salt

Water is also removed from microbial cells when they are placed in solutions containing large quantities of salt. The salting of food, in addition to improving its flavor, prevents the microorganisms from reproducing.
Armand-Frappier Museum